Flux-creep in the second magnetization peak of BaFe{1.9}Ni{0.1}As2 superconductor

TL;DR

This study investigates flux-creep behavior in BaFe{1.9}Ni{0.1}As2 superconductors near the second magnetization peak, revealing three-dimensional pinning and complex vortex dynamics without a clear pinning mechanism change.

Contribution

It provides detailed flux-creep analysis across different field orientations, showing universal scaling and challenging existing pinning mechanism crossover models.

Findings

Pinning is three-dimensional across all orientations.

Flux-creep relaxation rates do not show features at the second magnetization peak.

No evidence of a pinning mechanism change at the peak field.

Abstract

Flux-creep data was obtained for fields along the second magnetization peak observed in M(H) curves of BaFe{1.9}Ni{0.1}As2 for H||c-axis. H||ab-planes and H forming a 45 degrees angle with ab-planes. The M-H loops from the different field directions can be collapsed onto a universal curve with a scaling factor equivalent to the superconducting anisotropy, showing that the pinning is three dimensional, although with remarkable differences in the vortex-dynamics as a function of field orientation. The resulting relaxation rate, R, when plotted as a function of field and temperature does not show any specific feature in the vicinity of the second magnetization peak field Hp, the relaxation shows a maximum at a field H_2 well above Hp for H||c and a minimum at H^* for fields well below Hp for H||ab$ and H$-45-ab. Isofield plots of the scaled activation energy obtained from flux-creep data at several different temperatures also do not show any evidence of a change in the pinning mechanism as the peak field is crossed. The Hp lines in the resulting phase diagrams do not appear to be consistent with a description-terms of a collective-plastic pinning crossover.